1. Field of the Invention:
The invention is directed to a method for precise positioning of a magnetic head to various tracks of a magnetic tape in a magnetic tape recorder wherein the magnetic head is displaceable back and forth perpendicular to the moving direction of the magnetic tape for positioning to the various tracks, and wherein the magnetic head has at least one write head and one allocated read head. The invention is also directed to an arrangement for the implementation of the method.
2. Description of the Prior Art:
German published application No. 32 44 149 discloses an arrangement for positioning a magnetic head to various tracks of a magnetic tape wherein the magnetic tape is accommodated in a cassette which is inserted into the magnetic tape recorder means in a longitudinal direction. The magnetic tape is moved in a longitudinal direction by use of a tape drive roller, and the recording on a plurality of parallel tracks occurs by use of a magnetic head. For example, the magnetic head is provided with two write/read heads arranged above one another and the recording occurs in four parallel tracks. The magnetic head is positioned to the various tracks by use of a positioning means. The positioning means contains an electric motor designed as a stepping motor at which a worm gearing is arranged. This worm gear cooperates with a screw gearing via which a magnetic head carrier accepting the magnetic head is displaced perpendicular to the moving direction of the magnetic tape.
Although precise component parts are employed for the positioning means, a deviation of a write/read head from the exact center of a track is possible when the magnetic head is positioned to the outer tracks. In magnetic tape recorders having a low number of tracks, this deviation presents no difficulties in recording or playback of data signals. When, however, the number of tracks on the same magnetic tape is increased, such deviations cannot be accepted.
European patent application No. 86100172.5 discloses a method wherein the mechanical tolerances of the positioning means are compensated such that the precise positions of a write head or read head to the centers of the tracks on the magnetic tape are identified during a measuring event on the basis of a positioning to at least one track. The identified positions are assigned position values for the electric motor which are then taken into consideration during normal operation of the magnetic tape recorder. In this known method, however, only position values which occur due to tolerances in the positioning means are identified.
However, other deviations which are not covered by the known method can arise in magnetic heads and in their adjustment. The magnetic head shown in FIG. 1 is adjusted in a magnetic tape recorder in the ideal case such that column lines G1 and G2 which proceed perpendicular to the moving direction of a magnetic tape (not shown) are also exactly perpendicular to a reference plane B which, for example, can be the base plate of a cassette accepting the magnetic tape. The magnetic head 1 contains two write heads W and W1, and contains two read heads R or R1 allocated thereto which should be arranged at a rated distance D from one another. However, this distance D is not always precisely observed during manufacture of the magnetic heads, so that the actual distance amounts to D+a, whereby a can be positive or negative. In a recording with the write head W, the tape as indicated by an arrow is moved from right to left, whereas the magnetic tape is moved from left to right given recording with the write head W1. The write head W or W1 can be arranged offset in a perpendicular direction with respect to the moving direction of the magnetic tape with reference to the read head R or R1 as a consequence of manufacturing tolerances, mainly by a value b or b1, both of which can likewise be positive or negative. The result thereof is that the tracks do not always lie precisely in the center of the read heads R or R1 given a recording with the write heads W or W1.
It is also assumed in the illustration in FIG. 2 that the magnetic head 1 can be arranged turned by an angle alpha relative to the reference surface B. For reasons of clarity, this angle has been shown exaggerated in size in FIG. 2. This turning is likewise expressed in an offset c or cl of the write heads W or W1 relative to the read heads R or R1.
A further offset of the tracks can occur since the magnetic tape within the guideposts of the magnetic tape recorder or of the cassette shifts perpendicular to the running direction of the magnetic tape dependent on this running direction.
These different positions of the tracks during writing and during reading are not taken into consideration by the known method.